Imaging device and electronic apparatus

ABSTRACT

An imaging device includes: a photoelectric conversion region that generates photovoltaic power for each pixel depending on irradiation light; and a first element isolation region that is provided between adjacent photoelectric conversion regions in a state of surrounding the photoelectric conversion region.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of ProvisionalApplication Ser. No. 61/929,842, filed Jan. 21, 2014, the entirecontents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an imaging device and an electronicapparatus, and specifically, to an imaging device and an electronicapparatus that can solve a problem such as blooming due to a PN junctiondiode.

In the related art, a charge accumulation type imaging device(hereinafter, referred to as an accumulation type imaging device) as animaging device equipped in an electronic apparatus having an imagingfunction represented by a digital camera is known.

In the accumulation type imaging device, when excessive light isincident and an accumulation charge amount exceeds a saturation chargeamount, an excess portion of a signal charge flows into an N-typesubstrate beyond an overflow barrier or flows into floating diffusionbeyond a potential barrier under a transfer gate. Therefore, since adynamic range of the accumulation type imaging device is limited by thesaturation charge amount of a charge accumulation region, it isdifficult to realize a large dynamic range and, as a result, there is aproblem that overexposure or underexposure is likely to occur.

Thus, as a solid-state imaging device capable of solving such a problem,a logarithmic sensor configured of photovoltaic type pixels is proposed(for example, see EP1354360 and US2011/0025898A1).

FIG. 1 illustrates an equivalent circuit for one pixel of thephotovoltaic type pixel configuring the logarithmic sensor (EP1354360,FIG. 5).

In a photovoltaic type pixel 1, photovoltaic power proportional to alogarithm of a photocurrent value depending on incident light 2 isgenerated by a PN junction diode 3, the photovoltaic power that isgenerated is amplified by an amplifier 4 and becomes an image signal,and the image signal that is generated is output to a vertical signalline 7 through a switch 6. Moreover, the PN junction diode 3 is reset bya switch 5.

As described above, in the photovoltaic type pixel 1, since the imagesignal that is generated is output to a subsequent stage without beingaccumulated, even when excessive incident light 2 is incident, the pixelsignal is not saturated.

Moreover, the photovoltaic type pixel 1 can be operated as anaccumulation type.

SUMMARY

However, as a result of analysis of the photovoltaic type pixel 1, thefollowing disadvantages are found.

A first disadvantage is the blooming. FIG. 2 is a cross-sectional viewillustrating an example of a pixel structure of the photovoltaic typepixel illustrated in FIG. 1 and illustrates an overview of theoccurrence of the blooming.

Specifically, when the photovoltaic power is generated corresponding tothe incident light 2, the PN junction diode that is a photo-sensor isbiased in a forward direction and, as a result, since electrons diffusefrom an N-type region into a P-type substrate, as represented by a dotline A of FIG. 2, the electrons which are diffused may reach theadjacent photo-sensor (PN junction diode). In this case, since theadjacent pixel is also the photovoltaic type pixel, the blooming occurs.Moreover, although not illustrated, even if the adjacent pixel of thephotovoltaic type pixel 1 is the accumulation type pixel, the bloomingoccurs similarly.

A second disadvantage is that temperature change of the pixel signalamount is large. A pixel signal voltage V_(PD) can be represented by thefollowing Expression (1).

$\begin{matrix}{V_{PD} = {{- \frac{kT}{q}}{\ln \left( {\frac{I_{\lambda}}{I_{S}} + 1} \right)}}} & (1)\end{matrix}$

Here, I_(λ) is the photocurrent, I_(s) is a reverse saturated current inthe PN junction diode 3 and is a value that exponentially increases withthe increase of the temperature. Thus, when I_(s) exponentiallyincreases with the increase of the temperature, the pixel signal voltageV_(PD) is remarkably decreased.

The description will be explained in more detail. FIG. 3 illustrates arelationship between illuminance (standardized) of the incident light ateach temperature of the photovoltaic type pixel 1 illustrated in FIG. 1and an output voltage of the PN junction diode 3. It is understood fromFIG. 3 that the generated voltage remarkably decreases even in the sameilluminance when the temperature is decreased.

A third disadvantage is that low illuminance sensitivity is low andvariation suppression is difficult. As represented in Expression (1), inorder to increase the sensitivity, it is necessary to lower the I_(s).However, it is known that the I_(s) is increased by impuritycontamination or crystal defects and it is necessary to suppress those.However, it becomes costly to suppress all these because it takes a highdegree of process control.

A fourth disadvantage is that when a photovoltaic type pixel 1 operatesas the accumulation type, the dark current is increased.

FIG. 4 illustrates a relationship between irradiation time of thephotovoltaic type pixel 1 and the output voltage (US2011/0025898A1, FIG.2).

A case where the operation is performed as the accumulation typecorresponds to a Linear region of the same view and the occurrence ofthe dark current can be confirmed.

Description will be given in detail. FIG. 5 is an enlarged view when areverse bias is applied in the vicinity of the photo-sensor (the PNjunction diode 3) of the photovoltaic type pixel 1 illustrated inFIG. 1. When the photovoltaic type pixel 1 is operated as theaccumulation type, the photo-sensor is reverse biased and, in this case,since a depletion layer spreads as illustrated in the same view and thenSi/SiO₂ interface is positioned in the depletion layer, the dark currentis increased due to influence of the interface state.

In the present disclosure, it is desirable to realize an imaging devicethat is excellent in low illuminance sensitivity and low illuminance S/Nand of which sensitivity is less sensitive to a temperature whilerealizing a wide dynamic range.

According to a first embodiment of the present disclosure, there isprovided an imaging device including: a photoelectric conversion regionthat generates photovoltaic power for each pixel depending onirradiation light; and a first element isolation region that is providedbetween adjacent photoelectric conversion regions in a state ofsurrounding the photoelectric conversion region.

The imaging device according to the first embodiment of the presentdisclosure may further include a second element isolation region that isprovided between the photoelectric conversion region and a pixel circuitregion.

The first and second element isolation regions may be configured of amaterial that blocks a diffusion current.

A PN junction diode may be formed in the photoelectric conversion regionas a photo-sensor.

A transfer gate and floating diffusion may be further formed in thephotoelectric conversion region.

A photovoltaic type pixel and an accumulation type pixel may be formedin the adjacent photoelectric conversion regions.

In the first embodiment of the present disclosure, the photovoltaicpower is generated for each pixel depending on the irradiation light andthe diffusion current is blocked by the first element isolation regionprovided between the adjacent photoelectric conversion regions in astate of surrounding the photoelectric conversion region.

According to a second embodiment of the present disclosure, there isprovided an electronic apparatus equipped with an imaging device, inwhich the imaging device includes: a photoelectric conversion regionthat generates photovoltaic power for each pixel depending onirradiation light; and a first element isolation region that is providedbetween adjacent photoelectric conversion regions in a state ofsurrounding the photoelectric conversion region.

In the second embodiment of the present disclosure, with the imagingdevice of the electronic apparatus, the photovoltaic power is generatedfor each pixel depending on the irradiation light and the diffusioncurrent is blocked by the first element isolation region providedbetween the adjacent photoelectric conversion regions in a state ofsurrounding the photoelectric conversion region.

According to the first embodiment of the present disclosure, it ispossible to suppress the blooming between the pixels.

According to the second embodiment of the present disclosure, it ispossible to obtain an image with excellent sensitivity and S/N in lowilluminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating an equivalent circuit for onepixel of a photovoltaic type pixel configuring a logarithmic sensor;

FIG. 2 is a cross-sectional view of a pixel structure corresponding tothe equivalent circuit of FIG. 1;

FIG. 3 is a view illustrating a voltage generated at each temperaturefor the same illuminance;

FIG. 4 is a view illustrating a relationship between irradiation time ofa photovoltaic type pixel and an output voltage;

FIG. 5 is a view illustrating spread of a depletion layer generated in aphoto-sensor in a reverse bias;

FIG. 6 is a circuit diagram illustrating an equivalent circuit of aphotovoltaic type pixel that is a first embodiment of the presentdisclosure;

FIG. 7 is a top view of a pixel structure corresponding to thephotovoltaic type pixel of FIG. 6;

FIG. 8 is a cross-sectional view of a pixel structure corresponding tothe photovoltaic type pixel of FIG. 6;

FIG. 9 is a cross-sectional view of a pixel structure corresponding tothe photovoltaic type pixel of FIG. 6;

FIG. 10 is a cross-sectional view illustrating a first configurationexample when the photovoltaic type pixel of FIG. 6 is applied to asurface irradiation type imaging device;

FIG. 11 is a cross-sectional view illustrating a second configurationexample when the photovoltaic type pixel of FIG. 6 is applied to asurface irradiation type imaging device;

FIG. 12 is a cross-sectional view illustrating a third configurationexample when the photovoltaic type pixel of FIG. 6 is applied to asurface irradiation type imaging device;

FIG. 13 is a cross-sectional view illustrating a fourth configurationexample when the photovoltaic type pixel of FIG. 6 is applied to asurface irradiation type imaging device;

FIG. 14 is a cross-sectional view illustrating a fifth configurationexample when the photovoltaic type pixel of FIG. 6 is applied to a backsurface irradiation type imaging device;

FIG. 15 is a cross-sectional view illustrating a sixth configurationexample when the photovoltaic type pixel of FIG. 6 is applied to a backsurface irradiation type imaging device;

FIG. 16 is a cross-sectional view illustrating a seventh configurationexample when the photovoltaic type pixel of FIG. 6 is applied to a backsurface irradiation type imaging device;

FIG. 17 is a circuit diagram illustrating an equivalent circuit of anaccumulation type and photovoltaic type pixel that is a secondembodiment of the present disclosure;

FIG. 18 is a top view of a pixel structure of the accumulation type andphotovoltaic type pixel of FIG. 17;

FIG. 19 is a cross-sectional view of a pixel structure corresponding tothe accumulation type and photovoltaic type pixel of FIG. 17;

FIGS. 20A and 20B are potential distribution views of the accumulationtype and photovoltaic type pixel of FIG. 17;

FIG. 21 is a timing chart when the accumulation type and photovoltaictype pixel of FIG. 17 is operated as an accumulation type pixel;

FIG. 22 is a timing chart when the accumulation type and photovoltaictype pixel of FIG. 17 are operated as a photovoltaic type pixel;

FIG. 23 is a cross-sectional view illustrating an eighth configurationexample when the accumulation type and photovoltaic type pixel of FIG.17 are applied to the surface irradiation type imaging device;

FIG. 24 is a cross-sectional view illustrating a ninth configurationexample when the accumulation type and photovoltaic type pixel of FIG.17 are applied to the back surface irradiation type imaging device;

FIGS. 25A to 25C are equivalent circuits illustrating a configurationexample capable of employing an amplifier in the accumulation type andphotovoltaic type pixel of FIG. 17;

FIG. 26 is a view illustrating output voltage characteristics of a PNjunction diode;

FIG. 27 is a view illustrating simulation results of an output voltageof a FD; and

FIG. 28 is a view illustrating an outline of a calibration method of anoutput value of the photovoltaic type pixel.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a best mode (hereinafter, referred to as an embodiment) forimplementing the present disclosure is described in detail withreference to the drawings. Moreover, the description is performed in thefollowing order.

1. First Embodiment

2. Second Embodiment

1. First Embodiment

A photovoltaic type pixel according to a first embodiment will bedescribed with reference to the drawings. Moreover, the same referencenumerals are appropriately given to common portions in each view.

FIG. 6 illustrates an equivalent circuit of a photovoltaic type pixelaccording to the first embodiment. A photovoltaic type pixel 10 has a PNjunction diode 11, an amplifier 12 and a switch 13. The PN junctiondiode 11 generates photovoltaic power in proportion to a logarithm of aphotocurrent value depending on incident light. The amplifier 12amplifies the generated photovoltaic power and outputs a pixel signalobtained as a result thereof to a subsequent stage. The switch 13 resetsthe PN junction diode 11.

FIG. 7 illustrates an arrangement view of an upper surface for 2×2pixels of a pixel structure corresponding to the photovoltaic type pixel10 of which the equivalent circuit is illustrated in FIG. 6. Asillustrated in the same view, the photovoltaic type pixel 10 isconfigured of a photoelectric conversion region 21 and a pixel circuitregion 22 which are isolated by an element isolation region 35. The PNjunction diode 11 of FIG. 6 is formed in the photoelectric conversionregion 21 and an amplifier 4, a switch 5, a MOS Tr. 36 (FIG. 11), andthe like besides the PN junction diode 11 are formed in the pixelcircuit region 22.

FIG. 8 illustrates a cross section of the pixel structure in lineVIII-VIII of FIG. 7 and FIG. 9 illustrates a cross section of the pixelstructure in line IX-IX of FIG. 7. As is apparent from the crosssections of FIGS. 8 and 9, isolation between the photoelectricconversion region 21 and the photoelectric conversion region 21, andbetween the photoelectric conversion region 21 and the pixel circuitregion 22 is performed by the element isolation region 35.

Specifically, as illustrated in FIG. 9, the PN junction diode 11 formedin the photoelectric conversion region 21 is configured of a P-typeregion 31, an N-type region 32, an electrode 33 for ohmic contact withthe P-type region 31, and an electrode 34 for ohmic contact with theN-type region 32.

For example, the P-type region 31 is a semiconductor of IV groups suchas Si and Ge into which acceptor impurities are introduced, asemiconductor of III-V groups such as GaAs, InP, and InGaAs, or asemiconductor of II-VI groups selected from Hg, Cd, Te, Zn, and thelike.

For example, the N-type region 32 is a semiconductor of IV groups suchas Si and Ge into which donor impurities are introduced, a semiconductorof III-V groups such as GaAs, InP, and InGaAs, or a semiconductor ofII-VI groups selected from Hg, Cd, Te, Zn, and the like.

The electrodes 33 and 34 are selected depending on a material of theP-type region 31 or the N-type region 32 with which each of theelectrodes 33 and 34 comes into contact. For example, if the P-typeregion 31 and the N-type region 32 are Si, for example, an Al, Ti/Wlaminated film and the like are selected as the electrodes 33 and 34.

The element isolation region 35 is provided to suppress a leakagecurrent between the photoelectric conversion regions 21 (the PN junctiondiodes 11) which are adjacent to each other, and the photoelectricconversion region 21 and the pixel circuit region 22 which are adjacentto each other. Thus, the element isolation region 35 is disposed so asto surround a circumference of the photoelectric conversion region 21(the PN junction diode 11).

Moreover, at least one of element isolation regions 35 a and 35 ddisposed above and below the P-type region 31 has optical transparencyin order to cause the incident light to reach the PN junction diode 11.

The element isolation region 35 is configured of one of the followingmaterials or a combination thereof.

Insulating film (SiO₂, SiN, BSG, PSG, SiON, and the like)

Conductive semiconductor (for example, if the PN junction diode 11 isSi, n-Si and the like of a reverse conductive type with the P-typeregion 31)

Metal (an Ohmic Electrode and a Schottky Electrode for the P-Type Region31)

Moreover, the conductive semiconductor as the element isolation region35 may be the same material as the P-type region 31 or the N-type region32 of the PN junction diode 11, and is configured of a different type ofsemiconductor material and then may form a heterojunction. Otherwise,the same potential as the P-type region 31 of the PN junction diode 11is applied to the conductive semiconductor and the metal as the elementisolation region 35, and a thermal equilibrium state is formed betweenthe element isolation region 35 and the P-type region 31 of the PNjunction diode 11.

As described above, since electrons diffused from the N-type region 32to the P-type region 31 are prevented from reaching the adjacent pixelby providing the element isolation region 35, it is possible to suppressthe blooming to the adjacent pixel.

Specific Configuration Example of Photovoltaic Type Pixel 10 of FirstEmbodiment

FIG. 10 is a cross-sectional view of a configuration example(hereinafter, referred to as a first configuration example) in a casewhere the photovoltaic type pixel 10 of the first embodiment is appliedto a surface irradiation type imaging device.

The first configuration example is configured by laminating an epitaxialgrowth layer (epitaxial layer) 52, a wiring layer 54, and a condensinglayer 55 on an N-type substrate 51 in this order.

In the first configuration example, SiO₂ is used in the elementisolation region 35 a covering the upper side of the N-type region 32and a combination of SiO₂ and the conductive semiconductor (n-Si) isused in the element isolation regions 35 b and 35 c, and the N-typesubstrate 51 of the conductive semiconductor functions as the elementisolation region 35 d covering the lower side of the N-type region 32.

A manufacturing method of the first configuration example of FIG. 10will be described. First, the N-type epitaxial growth layer 52 of lowconcentration is laminated on the N-type substrate 51 by the existingmethod. Next, N-type impurity (for example, phosphorus or arsenic) andP-type impurity (for example, boron) are ion-implanted in the epitaxialgrowth layer 52, and activation annealing is performed by the existingmethod and then the P-type region and the N-type region (notillustrated) of high concentration are formed respectively in formingregions of an N-type region 53, the P-type region 31, the N-type region32, and the electrodes 33 and 34.

Next, an active element such as the MOS Tr. 36 and a passive elementsuch as MOS capacitance and diffusion layer resistance are formed in thepixel circuit region 22.

Subsequently, the region forming the element isolation regions 35 b and35 c of the epitaxial growth layer 52 is etched and SiO₂ is embeddedtherein, and the element isolation regions 35 b and 35 c are formed. Forthe etching, it is possible to use reactive ion etching, a method ofanodic oxidation, and the like. Furthermore, for the embedding of SiO₂,it is possible to use an ALD method, a CVD method, or a combination ofCMP technology after thermally oxidizing Si of the etching surface.

Next, the Si surface of the epitaxial growth layer 52 is thermallyoxidized, the element isolation region 35 a is formed and an oxide filmon the P-type region 31 and the N-type region 32 is removed by etching,and metal is embedded therein, and then the electrodes 33 and 34 areformed. For the metal that is embedded as the electrodes 33 and 34, forexample, it is possible to use Al, the Ti/W laminated film, and thelike.

Thereafter, the wiring layer 54 is formed by the existing method and,finally, the condensing layer 55 including an on-chip lens is formed bythe existing method.

Moreover, in FIG. 10, distribution of impurities within each of theP-type region 31 and the N-type region 32 is not illustrated, but inorder to increase the sensitivity, a width of the depletion layer formedbetween both sides is widened, the impurity concentration of a boundaryregion of both sides is decreased and then effective p-i-n junction maybe formed. In this case, an i layer may be a weak N-type layer or a weakP-type layer. However, in the configuration example of FIG. 10, theN-type region 32 is illustrated so as to be narrower than the P-typeregion 31, but when the weak N-type layer is provided, the N-type region32 is formed so as to be wider than the P-type region 31.

Next, FIG. 11 is a cross-sectional view of another configuration example(hereinafter, referred to as a second configuration example) in whichthe photovoltaic type pixel 10 of the first embodiment is applied to thesurface irradiation type imaging device.

In the second configuration example, SiO₂ is used in the elementisolation region 35 a covering the upper side of the N-type region 32and the conductive semiconductor (n-Si) is used in the element isolationregions 35 b and 35 c, and the N-type substrate 51 of the conductivesemiconductor (n-Si) functions as the element isolation region 35 dcovering the lower side of the N-type region 32.

An NMOS Tr. 36 a of the pixel circuit region 22 is formed in a p-well 57formed in the element isolation region 35 a.

In the second configuration example, since the N-type substrate 51 andthe element isolation regions 35 b and 35 c act as a drain of adiffusion current from the N-type region 32 to the P-type region 31, andthe diffusion current is inhibited from flowing to the adjacentphotoelectric conversion region 21, it is possible to suppress theblooming.

A manufacturing method of the second configuration example of FIG. 11will be described. First, the N-type epitaxial growth layer 52 of lowconcentration is laminated on the N-type substrate 51 by the existingmethod. Next, the N-type impurity (for example, phosphorus or arsenic)and the P-type impurity (for example, boron) are ion-implanted in theepitaxial growth layer 52, and activation annealing is performed by theexisting method and then the P-type region and the N-type region (notillustrated) of high concentration are formed respectively in formingregions of the P-type region 31, the N-type region 32, the elementisolation regions 35 c and 35 b, and the electrodes 33 and 34.

Next, the p-well 57 is formed in the element isolation region 35 c ofthe pixel circuit region 22 and the NMOS Tr. 36 a is formed in thep-well 57. Although not illustrated, when pMOS Tr. is formed, an n-wellis formed inside the p-well 57 and the pMOS Tr. is formed therein.

Next, the Si surface of the epitaxial growth layer 52 is thermallyoxidized, the element isolation region 35 a is formed and an oxide filmon the P-type region 31 and the N-type region 32 is removed by etching,and metal is embedded therein, and then the electrodes 33 and 34 areformed. For the metal that is embedded as the electrodes 33 and 34, forexample, it is possible to use Al, the Ti/W laminated film, and thelike.

Thereafter, the wiring layer 54 is formed by the existing method and,finally, the condensing layer 55 including the on-chip lens is formed bythe existing method.

Next, FIG. 12 is a cross-sectional view of still another configurationexample (hereinafter, referred to as a third configuration example) inwhich the photovoltaic type pixel 10 of the first embodiment is appliedto the surface irradiation type imaging device.

In the third configuration example, SiO₂ is used in the elementisolation region 35 a, a metal layer is used in the element isolationregions 35 b and 35 c, and the N-type substrate 51 of the conductivesemiconductor (n-Si) is used as the element isolation region 35 d. As amaterial of the metal layer of the element isolation regions 35 b and 35c, it is preferable to use metal that does not degrade a carrierlifetime of the P-type region 31 and the N-type region 32. Furthermore,metal is preferable that forms the Schottky junction with the elementisolation region 35 d and inhibits the leakage current from flowing from35 b and 35 c to 35 d. Otherwise, at least the insulating film such asSiO₂ is formed on the interface of 35 d, 35 b and 35 c, and the leakagecurrent may be inhibited from flowing from 35 b and 35 c to 35 d. Themetal layer is connected to the P-type region 31 and has the samepotential, and an electrically neutral region of the P-type region 31becomes the thermal equilibrium state with the metal layer.

Therefore, since the current flowing between the metal layer and theP-type region 31 becomes zero in the low illumination, it is possible tosuppress the decrease of the sensitivity of the low illuminance due tothe leakage current.

For the manufacturing method of the third configuration example of FIG.12, the embedding process of SiO₂ as the element isolation regions 35 band 35 c in the manufacturing method of the first configuration exampleof FIG. 10 may be replaced with the embedding process of the metallayer. Furthermore, before embedding the metal, the insulating film suchas SiO₂ may be formed on the surfaces of 35 b and 35 c using thetechnology of the thermal oxidation, the ALD, or the like.

Next, FIG. 13 is a cross-sectional view of still yet anotherconfiguration example (hereinafter, referred to as a fourthconfiguration example) in which the photovoltaic type pixel 10 of thefirst embodiment is applied to the surface irradiation type imagingdevice. In the fourth configuration example, a photovoltaic type pixel61 (corresponding to the photovoltaic type pixel 10) and an accumulationtype pixel 62 are disposed in photoelectric conversion regions adjacentto each other across the pixel circuit region 22.

Moreover, the photovoltaic type pixel 61 of FIG. 13 is the same as thefirst configuration example illustrated in FIG. 10, but may employ thesecond configuration example illustrated in FIG. 11 or the thirdconfiguration example illustrated in FIG. 12. On the other hand, for theportion of the accumulation type pixel 62, it is possible to apply theexisting configuration as illustrated in FIG. 13.

As illustrated in the view, a PN junction region of the photovoltaictype pixel 61 is surrounded by the element isolation regions 35 a, 35 b,35 c, and 35 d, but it is not necessary for areas between the followingregions to be surrounded by the element isolation regions 35 b and 35 c:

Between the photoelectric conversion region of the accumulation typepixel 62 and the photoelectric conversion region of the adjacentaccumulation type pixel 62;

Between the photoelectric conversion region of the accumulation typepixel 62 and the pixel circuit region 22 of the accumulation type pixel62;

Between the photoelectric conversion region of the accumulation typepixel 62 and the pixel circuit region of the adjacent photovoltaic typepixel 61.

For the manufacturing method of the fourth configuration example of FIG.13, the manufacturing process of the first configuration exampleillustrated in FIG. 10 may be added to the manufacturing method of theexisting accumulation type pixel 62.

Next, FIG. 14 is a cross-sectional view of a configuration example(hereinafter, referred to as a fifth configuration example) in which thephotovoltaic type pixel 10 of the first embodiment is applied to theback surface irradiation type imaging device.

In the fifth configuration example, the photoelectric conversion region21 and the pixel circuit region 22 are formed on the same substrate(sensor substrate 56). Each photoelectric conversion region 21 issurrounded by the element isolation regions 35 a, 35 b, 35 c, and 35 d,and the element isolation regions 35 a to 35 d are formed of SiO₂.

A manufacturing method of the fifth configuration example will bedescribed. First, a circuit substrate 58 in which a signal processingcircuit and the like are formed, and the sensor substrate 56 in whichthe pixel (photovoltaic type pixel) is formed are attached to each otherby the wiring layer 54, and the back surface of the sensor substrate 56is polished to a predetermined thickness. Next, a region of the sensorsubstrate 56 that forms the element isolation regions 35 b and 35 c isetched from the back surface side and SiO₂ is embedded, and then theelement isolation regions 35 b and 35 c are formed. Furthermore, a SiO₂oxide film is formed on the back surface of the sensor substrate 56 asthe element isolation region 35 d, and, finally, the condensing layer 55is laminated.

Moreover, for the polishing of the sensor substrate 56, for example, itis possible to apply the CMP method. For the etching of the sensorsubstrate 56, for example, it is possible to apply a reactiveion-etching method. For the embedment of SiO₂, it is possible to apply achemical vapor deposition method. Moreover, metal may be embeddedsimilar to the third configuration example illustrated in FIG. 12,instead of embedding SiO₂.

Next, FIG. 15 is a cross-sectional view of another configuration example(hereinafter, referred to as a sixth configuration example) in which thephotovoltaic type pixel 10 of the first embodiment is applied to theback surface irradiation type imaging device.

In the sixth configuration example, the photoelectric conversion region21 and the pixel circuit region (the MOS Tr. 36 and the like) are formedon different substrates (the sensor substrate 56 and the circuitsubstrate 58). Each photoelectric conversion region 21 is surrounded bythe element isolation regions 35 a, 35 b, 35 c, and 35 d, and theelement isolation regions 35 a and 35 d are formed of SiO₂, and theelement isolation regions 35 b and 35 c are formed by SiO₂ and theN-type region 53.

The N-type region 53 and the P-type region 31 of the sensor substrate 56are short-circuited by the electrode 33 and the thermal equilibriumstate is achieved between both sides. The electrode 33 is also connectedto a GND electrode (not illustrated) of the circuit substrate 58. TheN-type region 32 generating the photovoltaic power is connected to agate of the MOS Tr. 36 of the circuit substrate 58 by the electrode 34.

For the manufacturing method of the sixth configuration example, beforeforming the element isolation regions 35 b and 35 c with respect to themanufacturing method of the fifth configuration example illustrated inFIG. 14, the N-type region 53 is formed and the etching for the elementisolation regions 35 b and 35 c may be modified so as to stop at aposition in which the etching reaches the N-type region 53.

Moreover, in the sixth configuration example, a case where the sensorsubstrate 56 and the circuit substrate 58 are attached to each other bythe wiring layer 54 is illustrated, but surfaces of the sensor substrate56 and the circuit substrate 58 are bump-connected to each other byusing mounting technology and a configuration of a so-called hybridsensor may be employed.

Next, FIG. 16 is a cross-sectional view of still another configurationexample (hereinafter, referred to as a seventh configuration example) inwhich the photovoltaic type pixel 10 of the first embodiment is appliedto the back surface irradiation type imaging device. In the seventhconfiguration example, the photovoltaic type pixel 61 (corresponding tothe photovoltaic type pixel 10) and the accumulation type pixel 62 aredisposed in the adjacent photoelectric conversion regions.

Moreover, the photovoltaic type pixel 61 of FIG. 16 is the same as thesixth configuration example illustrated in FIG. 15, but may employ thefifth configuration example illustrated in FIG. 14. On the other hand,for the portion of the accumulation type pixel 62, it is possible toapply the existing configuration as illustrated in FIG. 16. Furthermore,as illustrated in FIG. 15, the electrode applying the potential to theelement isolation region of the P-type region 31 and the accumulationtype pixel 62 may be provided on the side of the circuit of the sensorsubstrate 56 or may be provided on the side of the incident surface ofthe light (neither of which is illustrated).

2. Second Embodiment

Next, a photovoltaic type pixel (hereinafter, referred to as anaccumulation type and photovoltaic type pixel) that can also be operatedas the accumulation type pixel of the second embodiment will bedescribed.

FIG. 17 illustrates an equivalent circuit of the accumulation type andphotovoltaic type pixel according to the second embodiment. Anaccumulation type and photovoltaic type pixel 70 is configured of a PNjunction diode 11, an amplifier 12, a TG 71, an FD 72, an RST 73, an RST74, and an Sel 75.

The PN junction diode 11 is configured of the P-type region 31 and theN-type region (charge accumulation region) 32 (all in FIG. 19), andperforms the photoelectric conversion depending on the incident light,and accumulates the signal charges generated as a result thereof orgenerates the photovoltaic power.

The TG 71 transfers the generated signal charges to the FD 72.Furthermore, the TG 71 transfers the generated photovoltaic power to theFD 72 by shorting the N-type region 32 in the FD 72 by a channel formedunder the TG 71.

The FD 72 is the N-type region and converts the signal charges into thesignal voltage. The RST 73 resets the FD 72 to a GND potential. The RST74 resets the FD 72 to a VDD potential. The amplifier 12 amplifies thepotential of the FD 72. The Sel 75 transfers an output signal of theamplifier 12 to a vertical signal line VSL.

FIG. 18 illustrates an arrangement view of an upper surface of 2×2pixels of a pixel structure corresponding to the accumulation type andphotovoltaic type pixel 70 of which the equivalent circuit isillustrated in FIG. 17. As illustrated in the same view, theaccumulation type and photovoltaic type pixel 70 is configured of aphotoelectric conversion region 21 and a pixel circuit region 22 whichare isolated by an element isolation region 35. The PN junction diode11, the TG 71, and the FD 72 of FIG. 17 are formed in the photoelectricconversion region 21 and the amplifier 12, the RST 73, the RST 74, theSel 75 and the like besides thereof are formed in the pixel circuitregion 22.

FIG. 19 illustrates a cross section of the pixel structure in lineXIX-XIX of FIG. 18. As illustrated in the same view, isolation betweenthe photoelectric conversion region 21 and the pixel circuit region 22is performed by the element isolation region 35.

As is apparent by comparing FIG. 19 and the cross-sectional views (FIGS.8 and 9) of the photovoltaic type pixel 10 of the first embodiment, theaccumulation type and photovoltaic type pixel 70 is structurallydifferent from the photovoltaic type pixel 10 in that the FD 72 isprovided inside thereof surrounded by the element isolation regions 35a, 35 b, 35 c, and 35 d, the electrode (ohmic electrode) 34 is connectedto the FD 72, and the TG 71 is provided for controlling the potentialbarrier between the FD 72 and the N-type region (charge accumulationregion) 32.

Next, FIGS. 20A and 20B are potential distribution views of theaccumulation type and photovoltaic type pixel 70, FIG. 20A correspondsto line A of FIG. 19 and FIG. 20B corresponds to line B of FIG. 19.Moreover, in FIGS. 20A and 20B, it is assumed that all element isolationregions 35 are SiO₂. As illustrated in the same view, it is preferablethat the height of the potential barrier of the circumference of theN-type region (charge accumulation region) 32 of the accumulation typeand photovoltaic type pixel 70 be substantially equal in any directionand be distributed to the height of the potential of a P-type neutralregion.

It is possible to operate the accumulation type and photovoltaic typepixel 70 illustrated in FIG. 17 as the accumulation type pixel or thephotovoltaic type pixel by the potential distribution.

FIG. 21 illustrates a timing chart when the accumulation type andphotovoltaic type pixel 70 is operated as the accumulation type pixel.Specifically, the TG 71 is turned OFF and the PN junction diode 11 isreset by the RST 74, and it is possible to be operated as theaccumulation type pixel.

FIG. 22 illustrates a timing chart when the accumulation type andphotovoltaic type pixel 70 is operated as the photovoltaic type pixel.Specifically, the TG 71 is turned ON and the PN junction diode 11 isreset by the RST 73, and it is possible to be operated as thephotovoltaic type pixel.

Moreover, when operating as the accumulation type pixel, since thecharges generated in the PN junction diode 11 are confined inside thepotential barrier having the same height in any direction, it ispossible to generate the same photovoltaic power as when operating asthe photovoltaic type pixel.

Furthermore, since the N-type region (charge accumulation region) 32 issurrounded by the P-type region 31 and the potential barrier under theTG 71, and does not come into contact with the interface of Si/SiO₂, thedark current can be suppressed similar to the accumulation type pixel ofthe related art and it is possible to obtain a good S/N even in the lowilluminance.

Furthermore, the same pixel may be operated while switching between theaccumulation type and the photovoltaic type. When operating the pixel byswitching to the photovoltaic type immediately after operating the pixelin the accumulation type, it is possible to shorten a Wait period beforereading the D phase by reversing the reading order of the P phase andthe D phase of FIG. 22.

Specific Configuration Example of Accumulation Type and PhotovoltaicType Pixel 70 of Second Embodiment

FIG. 23 is a cross-sectional view of a configuration example(hereinafter, referred to as an eighth configuration example) when theaccumulation type and photovoltaic type pixel 70 of the secondembodiment is applied to the surface irradiation type imaging device.

Moreover, the element isolation regions 35 a to 35 d of the eighthconfiguration example use the same material as that of the elementisolation regions 35 a to 35 d of the first configuration exampleillustrated in FIG. 10, but may be the same configuration as the elementisolation regions 35 a to 35 d of the second configuration exampleillustrated in FIG. 11 or the third configuration example illustrated inFIG. 12.

A manufacturing method of the eighth configuration example will bedescribed. It is possible to manufacture the eighth configurationexample by slightly correcting the manufacturing method of the surfaceirradiation type and accumulation type pixel (for example, theaccumulation type pixel 62 in the fourth configuration exampleillustrated in FIG. 13) of the related art as described below and byadding a forming process of the element isolation regions 35 a to 35 d.

Acceptor impurity is introduced into a region (a region between theN-type substrate 51 and the N-type region 32 in the P-type region 31)forming the overflow barrier in the accumulation type pixel of therelated art so as to form the P-type neutral region. Therefore, whenoperating the eighth configuration example as the photovoltaic typepixel, it is possible to generate the same photovoltaic power as that ofthe photovoltaic type pixel of the first embodiment.

The acceptor impurity is introduced into the P-type region 31 or a filmthat generates negative fixed charges is embedded inside SiO₂ of theelement isolation regions 35 b and 35 c so that hole concentration inthe vicinity of the interface of the P-type region 31 and the elementisolation regions 35 b and 35 c is set so as to have a predeterminedconcentration or more. As the film generating the negative fixedcharges, for example, it is possible to use a hafnium oxide film and asa film deposition method, it is possible to use a chemical vapordeposition method, a sputtering method, an atomic layer depositionmethod, and the like. Therefore, when operating the eighth configurationexample as the accumulation type pixel, it is possible to reduce thedark current to the same level as that of the accumulation type pixel ofthe related art.

Next, FIG. 24 is a cross-sectional view of a configuration example(hereinafter, referred to as a ninth configuration example) when theaccumulation type and photovoltaic type pixel 70 of the secondembodiment is applied to the back surface irradiation type imagingdevice.

Moreover, the element isolation regions 35 a to 35 d of the ninthconfiguration example use the same material as that of the elementisolation regions 35 a to 35 d of the sixth configuration exampleillustrated in FIG. 15, but may be the same configuration as the elementisolation regions 35 a to 35 d of the seventh configuration exampleillustrated in FIG. 16.

A manufacturing method of the ninth configuration example will bedescribed. It is possible to manufacture the ninth configuration exampleby slightly correcting the manufacturing method of the back surfaceirradiation type and accumulation type pixel of the related art asdescribed below and by adding a forming process of the element isolationregions 35 a to 35 d.

Acceptor impurity is introduced into the P-type region 31 or a film thatgenerates the negative fixed charges is embedded inside SiO₂ of theelement isolation regions 35 b and 35 c so that the hole concentrationin the vicinity of the interface of the P-type region 31 and the elementisolation regions 35 b and 35 c is set so as to have a predeterminedconcentration or more. As the film generating the negative fixedcharges, for example, it is possible to use a hafnium oxide film and asa film deposition method, it is possible to use a chemical vapordeposition method, a sputtering method, an atomic layer depositionmethod and the like. Therefore, when operating the ninth configurationexample as the accumulation type pixel, it is possible to reduce thedark current to the same level as that of the accumulation type pixel ofthe related art.

Configuration Example of Amplifier 12 of Equivalent Circuit ofAccumulation Type and Photovoltaic Type Pixel 70 of Second Embodiment

Next, FIGS. 25A to 25C illustrate three types of configuration examplescapable of employing the amplifier 12 in equivalent circuits of theaccumulation type and photovoltaic type pixel 70 illustrated in FIG. 17.Moreover, in a case of FIG. 25A or 25B, a signal voltage range ischanged depending on whether the accumulation type and photovoltaic typepixel 70 is operated as the accumulation type pixel or operated as thephotovoltaic type pixel. Thus, a back gate voltage or the like ischanged depending on whether to operate in either mode. Therefore, athreshold voltage of the Amp Tr. (the amplifier 12) is adjusted or alevel shifter is inserted between the TG 71 and the Amp Tr. (theamplifier 12).

Output voltage Characteristics of PN Junction Diode 11

Next, FIG. 26 illustrates simulation results of the output voltage ofthe PN junction diode 11 corresponding to a case where the voltage ofthe N-type substrate 51 is changed in the first configuration exampleillustrated in FIG. 10.

As illustrated in the same view, it is understood that the outputvoltage of the PN junction diode 11 is remarkably changed by thetemperature.

Output voltage Characteristics of FD 37

Next, FIG. 27 illustrates simulation results of the output voltage ofthe FD 72 corresponding to the irradiation light in a state where the TG71 is turned ON in the eighth configuration example illustrated in FIG.23. As illustrated in the same view, it is understood that the outputvoltage of the FD 72 logarithmically increases with respect to theilluminance. That is, it is understood that the eighth configurationexample is also operated as the photovoltaic type pixel.

Calibration of Output Value of Photovoltaic Type Pixel

FIG. 28 illustrates an outline of a calibration method of an outputvalue of the photovoltaic type pixel by using the output value of theaccumulation type pixel of the same pixel or the adjacent pixel.

First, in the same pixel in which the light amount is not saturated, alinear output value and a log output value are obtained. Next, the logoutput value is converted into the linear value and a calibrationcoefficient is determined so that the linear value after conversionmatches the linear output value. Finally, it is possible to obtain thelog output value after calibration by applying the determinedcalibration coefficient to the log output value of the adjacent pixelthat is saturated.

As described above, it is possible to obtain the output value that iscontinuous to the output value of the accumulation type pixel bycalibrating the log output value even when the output value of thephotovoltaic type pixel is changed by the temperature. Thus, it ispossible to suppress steps when synthesizing the image when operating asthe accumulation type pixel and the image when operating as thephotovoltaic type pixel.

Overview

As described above, according to the first and second embodiments, it ispossible to block the diffusion current by providing the elementisolation region and then it is possible to suppress the forward currentof PN junction diode from reaching the adjacent pixel.

Therefore, the blooming is suppressed in the vicinity of thephotovoltaic type pixel and, in the first embodiment, it is possible todispose the photovoltaic type pixel and the accumulation type pixeladjacent to each other without degrading the image quality or thesensitivity.

Furthermore, for example, it is possible to obtain the linear outputimage and the logarithmic output image in the same imaging device bydisposing the photovoltaic type pixel and the accumulation type pixeladjacent to each other without using an optical system that is largescale and expensive such as using a half mirror.

Then, it is possible to obtain the image in a wide luminance range withless noise by obtaining the linear output image and the logarithmicoutput image in the same imaging device without underexposing a lowluminance portion or overexposing a high luminance portion of theobject.

Furthermore, according to the second embodiment, since the same pixelcan be operated as the photovoltaic type pixel and the accumulation typepixel without increasing the dark current, it is possible to synchronizethe image by using the linear output value in the low luminance portionand using the log output value in the high luminance portion of theobject. Therefore, it is possible to obtain the linear output image andthe log output image without sacrificing the resolution.

Furthermore, when calibrating the log output value by using the linearoutput value, it is possible to cancel the change in the log outputvalue caused by the temperature. Thus, it is possible to reduce thesteps in the interface between the linear output image and the logoutput image.

Moreover, the first and second embodiments described above can beapplied to any electronic apparatus having an imaging function inaddition to the imaging apparatus represented by a digital camera.

Furthermore, embodiments of the present disclosure are not limited tothe embodiments described above and various modifications are possiblewithout departing from the scope of the present disclosure.

The present disclosure can take the following configurations.

(1) An imaging device including: a photoelectric conversion region thatgenerates photovoltaic power for each pixel depending on irradiationlight; and a first element isolation region that is provided betweenadjacent photoelectric conversion regions in a state of surrounding thephotoelectric conversion region.

(2) The imaging device according to (1), further including: a secondelement isolation region that is provided between the photoelectricconversion region and a pixel circuit region.

(3) The imaging device according to (2), in which the first and secondelement isolation regions are configured of a material that blocks adiffusion current.

(4) The imaging device according to any one of (1) to (3), in which a PNjunction diode is formed in the photoelectric conversion region as aphoto-sensor.

(5) The imaging device according to any one of (1) to (4), in which atransfer gate and floating diffusion are further formed in thephotoelectric conversion region.

(6) The imaging device according to any one of (1) to (5), in which aphotovoltaic type pixel and an accumulation type pixel are formed in theadjacent photoelectric conversion regions.

(7) An electronic apparatus equipped with an imaging device, in whichthe imaging device includes: a photoelectric conversion region thatgenerates photovoltaic power for each pixel depending on irradiationlight; and a first element isolation region that is provided betweenadjacent photoelectric conversion regions in a state of surrounding thephotoelectric conversion region.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An imaging device comprising: a photoelectricconversion region that generates photovoltaic power for each pixeldepending on irradiation light; and a first element isolation regionthat is provided between adjacent photoelectric conversion regions in astate of surrounding the photoelectric conversion region.
 2. The imagingdevice according to claim 1, further comprising: a second elementisolation region that is provided between the photoelectric conversionregion and a pixel circuit region.
 3. The imaging device according toclaim 2, wherein the first and second element isolation regions areconfigured of a material that blocks a diffusion current.
 4. The imagingdevice according to claim 2, wherein a PN junction diode is formed inthe photoelectric conversion region as a photo-sensor.
 5. The imagingdevice according to claim 4, wherein a transfer gate and floatingdiffusion are further formed in the photoelectric conversion region. 6.The imaging device according to claim 5, wherein a photovoltaic typepixel and an accumulation type pixel are formed in the adjacentphotoelectric conversion regions.
 7. An electronic apparatus equippedwith an imaging device, wherein the imaging device includes: aphotoelectric conversion region that generates photovoltaic power foreach pixel depending on irradiation light; and a first element isolationregion that is provided between adjacent photoelectric conversionregions in a state of surrounding the photoelectric conversion region.